docs: def download_example_datasets(self):
          """ Download example datasets from `openSNP <https://opensnp.org>`_.
  
          Per openSNP, "the data is donated into the public domain using `CC0 1.0
          <http://creativecommons.org/publicdomain/zero/1.0/>`_."
  
          Returns
          -------
          paths : list of str or None
              paths to example datasets
  
          References
          ----------
          ..[1] Greshake B, Bayer PE, Rausch H, Reda J (2014), "openSNP-A Crowdsourced Web Resource
            for Personal Genomics," PLOS ONE, 9(3): e89204,
            https://doi.org/10.1371/journal.pone.0089204
          """
          paths = []
          paths.append(
              self._download_file(
                  "https://opensnp.org/data/662.23andme.304",
                  "662.23andme.304.txt.gz",
                  compress=True,
              )
          )
          paths.append(
              self._download_file(
                  "https://opensnp.org/data/662.23andme.340",
                  "662.23andme.340.txt.gz",
                  compress=True,
              )
          )
          paths.append(
              self._download_file(
                  "https://opensnp.org/data/662.ftdna-illumina.341",
                  "662.ftdna-illumina.341.csv.gz",
                  compress=True,
              )
          )
          paths.append(
              self._download_file(
                  "https://opensnp.org/data/663.23andme.305",
                  "663.23andme.305.txt.gz",
                  compress=True,
              )
          )
  
          # these two files consist of concatenated gzip files and therefore need special handling
          paths.append(
              self._download_file(
                  "https://opensnp.org/data/4583.ftdna-illumina.3482",
                  "4583.ftdna-illumina.3482.csv.gz",
              )
          )
          paths.append(
              self._download_file(
                  "https://opensnp.org/data/4584.ftdna-illumina.3483",
                  "4584.ftdna-illumina.3483.csv.gz",
              )
          )
  
          try:
              for gzip_path in paths[-2:]:
                  # https://stackoverflow.com/q/4928560
                  # https://stackoverflow.com/a/37042747
                  with open(gzip_path, "rb") as f:
                      decompressor = zlib.decompressobj(31)
  
                      # decompress data from first concatenated gzip file
                      data = decompressor.decompress(f.read())
  
                      if len(decompressor.unused_data) > 0:
                          # decompress data from second concatenated gzip file, if any
                          additional_data = zlib.decompress(decompressor.unused_data, 31)
                          data += additional_data[33:]  # skip over second header
  
                  # recompress data
                  with gzip.open(gzip_path, "wb") as f:
                      f.write(data)
          except Exception as err:
              print(err)
  
          return paths